Salivary cells were isolated from the gland of rats (1, 7, 14 and 21 days old) by enzymic digestion. They formed small aggregates with typical morphological characteristics and were functional units with characteristic 36Cl fluxes. The rates of isotopic uptake in the absence of secretagogue (basal uptake) were similar at all ages. Uptake was time-dependent, leading to a steady-state isotope content of 6.7-8.9 nmol/mg protein after 3-5 min of incubation. 36Cl accumulation (uptake) in the unstimulated condition was inhibited 33-39 per cent by exposure to 1 mM furosemide at all ages, but was reduced significantly less (50 per cent) by 1 microM acetylcholine in cells of 1-day-old animals than in older ones. In aggregates exposed to 36Cl for 12 min (preloaded with tracer), acetylcholine caused a net efflux of isotope which was significantly less in cells of 1-day-old rats (18 versus 35 per cent in cells of older animals). Thus it was shown (1) that functional cell aggregates can be obtained from early postnatal rats; (2) that when not stimulated, their time-dependent Cl accumulation is partially inhibited by loop diuretics, and so likely to involve a cation/anion cotransport system; and (3) that Cl efflux, which may occur by way of membrane channels, is significantly reduced early in the postnatal period. The putative Cl channels are therefore either not fully developed, or they do not become responsive to stimulation until later. This reduced Cl efflux could be related to differences in Ca2+ mobilization at early and late phases of postnatal glandular development as Cl efflux is a Ca2+-dependent phenomenon in salivary cells.